1. Field of the Invention
This invention relates to an automatic piloting device for an aerodyne such as e.g. a helicopter.
The purpose of such devices is generally to unburden the pilot of a certain number of tasks while improving the flight characteristics of the aerodyne which is usually unstable, and while performing certain piloting tasks such as the maintaining of the aerodyne on a certain trajectory selected by the pilot.
The aim of the automatic piloting devices intended to equip helicopters is more particularly to improve the stability of the aircraft during manual piloting, and to provide the pilot with an impression of greater stability and homogeneity as regards the characteristics of the effects of the different flight control surfaces.
2. Description of the Prior Art
Up to now, these devices carried out, for each of the three piloting axes (roll, pitch and yaw), an analog computation enabling controlling of the set of actuators acting on the flight control surfaces as a function of commands from the pilot and the information provided by the sensors.
Generally, the actuators for a piloting axis comprise a low-authority series thrustor with very fast motion, and a trim thrustor with full authority and slower motion, intended to recenter the position of the series thrustor.
When failure on a piloting axis entails fast and major movements of the helicopter, or when the mission entrusted to it requires considerable attention on the part of the crew, a redundant system is used to obtain the level of safety required. To this end, the computation sequence for each piloting axis is doubled and two actuators are installed in series on the rods of each flight control surface. In this way, if one of the two command sequences of a piloting axis breaks down, the other sequence counters it, and if the faulty command sequence is put out of operation, the mission can be continued.
This latter solution has the drawback of increasing the space requirements of the automatic piloting device and of multiplying the cost thereof.
Moreover, in a device using a digital computer controlling the piloting of several flight control axes, and in the event of failure thereof, the automatic piloting device is no longer operational for any of the piloting axes. This solution is therefore unacceptable in the context of certain missions and for certain types of helicopters.
In order to solve this problem, a second computer can be installed in parallel to the first one. In this way, if one of the computers breaks down, the other one continues the automatic piloting.
Should the required safety restrictions impose that the aircraft be equipped with an automatic piloting device capable of automatic reconfiguring, three computers operating in parallel can be used to determine the faulty computer and to perform automatic piloting functions in all circumstances.
These solutions also have the drawback of multiplying the cost of such a device.